In vivo reprogramming of cytotoxic effector CD8 T cells via fractalkine-conjugated mRNA-LNPs

Selective in vivo reprogramming of cytotoxic effector CD8 T (T_eff) cells holds tremendous promise as a therapeutic tool but has not yet been accomplished. Here, we demonstrate that fractalkine-conjugated mRNA lipid nanoparticles (mRNA-LNPs) can specifically target and deliver mRNA to CX3CR1⁺ T_eff cells in vitro and in vivo. In mice, fractalkine-conjugated mRNA-LNPs targeted up to 95% of blood and splenic T_eff cells. In addition, delivery of IL-2-encoding mRNA and human CD62L-encoding mRNA to mouse T_eff cells enabled robust exogenous IL-2 secretion and CD62L expression. In rhesus macaques, fractalkine-conjugated mRNA-LNPs targeted up to ~100% of peripheral blood T_eff cells, and delivery of human CD62L-encoding mRNA enabled cell-surface human CD62L expression on peripheral blood T_eff cells and detection of human CD62L⁺ T_eff cells in lymphoid tissue. Collectively, these data demonstrate the potential of natural receptor ligand-based targeting of mRNA-LNPs for rapid, efficient, and transient in vivo modification of T_eff cells.